Because of their excellent properties, ethylene copolymers have been molded by various methods and applied to various uses. However, the ethylene copolymers have poor affinity for metals and various polar materials, because they have no polar group in their molecules, that is, they are non-polar resins. Therefore, when the ethylene copolymers are applied to uses where they must be bonded to metals or blended with polar resins, some improvement should be made. In order to improve their affinity for the polar materials, for example, a method of graft-modifying the ethylene copolymers with polar monomers is known.
However, even the graft-modified ethylene copolymers show insufficient adhesive strength to polystyrene resins, ABS resin, polyacrylonitrile resins, polyester resins, polycarbonate resins, polyvinylidene chloride resins, etc.
In this connection, Japanese Patent Laid-Open Publication No. 241144/1986 describes that a composition comprising a low-density ethylene/.alpha.-olefin copolymer having been partially or wholly graft-modified with an unsaturated carboxylic acid or its derivative and a tackifier shows good adhesive strength to styrene resins.
Japanese Patent Laid-Open Publications No. 045445/1989 and No. 029331/1990 describe that an adhesive resin composition comprising a low-density ethylene/.alpha.-olefin copolymer, an ethylene/vinyl acetate copolymer and polyethylene having been partially or wholly graft-modified with an unsaturated carboxylic acid or its derivative shows good adhesive strength to polyester resins, polycarbonate resins, polyvinylidene chloride resins, etc.
However, the low-density ethylene/.alpha.-olefin copolymers shown in these publications sometimes exhibit insufficient adhesive strength in an atmosphere of high temperatures.
Accordingly, if adhesive ethylene copolymer resin compositions, which have good adhesive strength to polystyrene resins, ABS resin, polyacrylonitrile resins, polyester resins, polycarbonate resins, polyvinylidene chloride resins, etc. and are hardly decreased in the adhesive strength even in an atmosphere of high temperatures, are developed, their industrial value will be extremely high.
The ethylene copolymers are required to have different properties according to the molding method or use purpose. For example, in the high-speed production of inflation films, an ethylene copolymer having a high melt tension for the molecular weight must be selected to conduct stable high-speed molding without suffering instability of bubbles or break of bubbles. The similar properties are required to prevent sagging or break of resin in the hollow molding or to restrain neck-in to a minimum in the T-die molding. In the extrusion molding, further, the ethylene copolymer is required to have a small stress in a high-shear state from the viewpoints of improvement in qualities of molded products and economical efficiency such as reduction of power consumption in the molding process.
Meanwhile, a method of improving a melt tension or a swell ratio (die swell ratio) of the ethylene polymers obtained by the use of Ziegler catalysts, particularly titanium catalysts, to thereby improve moldability is proposed in Japanese Patent Laid-Open Publications No. 90810/1981 and No. 106806/1985. However, the ethylene polymers, specifically low-density ethylene polymers, obtained by the use of the titanium catalysts generally have problems of wide composition distribution and surface tackiness of their molded products such as films.
Of the ethylene polymers prepared by the use of Ziegler catalysts, those prepared by the use of chromium catalysts have relatively good melt tension but has a problem of poor heat stability. The reason is presumably that the ends of chain molecules of the ethylene polymers prepared by the use of the chromium catalysts easily become unsaturated bonds.
The ethylene polymers obtained by the use of metallocene catalysts among the Ziegler catalysts are known to have advantages such as narrow composition distribution and low surface tackiness of their molded products such as films. In Japanese Patent Laid-Open Publication No. 35007/1985, however, it is described that the ethylene polymers obtained by using, as catalysts, zirconocene compounds composed of cyclopentadiene derivatives contain one terminal unsaturated bond per one molecule, and therefore it is thought that they have bad heat stability, similarly to the ethylene polymers obtained by the use of the chromium catalysts. Additionally, there is a fear of bad flowability in the extrusion molding process because these ethylene polymers have narrow molecular weight distribution.
Accordingly, if ethylene polymers having high melt tension, small stress in the high-shear region, good heat stability, excellent mechanical strength and narrow composition distribution is developed, their industrial value will be extremely high.
The present invention is intended to solve such problems associated with the prior art as described above, and it is an object of the invention to provide adhesive ethylene copolymer resin compositions having high adhesive strength to polystyrene resins, ABS resin, polyacrylonitrile resins, polyester resins, polycarbonate resins and polyvinylidene chloride resins even in an atmosphere of high temperatures, and to provide laminates using the compositions.
It is another object of the invention to provide adhesive ethylene copolymer resin compositions having excellent heat stability, moldability and transparency and capable of forming film layers of high adhesive strength to metals and materials of high polarity, and to provide laminates using the compositions.